The present invention relates generally to the field of wireless communications and in particular to methods of forward link admission control.
The 3rd Generation (3G) wireless communication networks provide mobile users wireless access to packet data networks, such as the Internet. Many applications and services, once available only to users at fixed terminals, are now being made available via wireless communication networks to mobile users. Real-time streaming video and music, on-line interactive gaming, text messaging, email, web browsing and Voice over IP (VoIP), are just a few examples of data services now being provided via wireless networks to mobile users.
The demand for such wireless data services has led to the development of high speed packet data channels to provide the high data rates that such services require. High speed packet data channels are employed on the forward link in cdma2000 (both 1xEV-DV and 1x-EV-DO) and High Speed Downlink Packet Data Access (HSPDA) systems. The high speed packet data channel is a shared channel. In 1xEV-DV systems, the forward link packet data channel is known as the Forward Packet Data Channel (F-PDCH). Transmissions from a base station to the mobile stations are time-multiplexed and transmitted at full power. At any given time, the base station transmits to only one mobile station.
The slot times and data rates allocated for transmissions to the mobile stations depend on the channel conditions seen by each mobile station. The mobile stations measure the signal quality on the forward link and send channel quality information on the reverse link overhead channels to the base station. The channel quality information may comprise either a channel quality indicator (CQI) in 1xEV-DV and HSPDA, or a data rate indication (DRC) in 1xEV-DO. The base station selects a forward link data rate and assigns slot times for a mobile station based on the channel quality feedback from that mobile station. The base stations may also vary the modulation and encoding used for the forward link channel, depending on the channel conditions and/or the requested data rate.
The base station transmits to only one mobile station at a time on the forward link packet data channel(s). The mobile station is selected from a plurality of mobile stations requesting packet data according to a variety of criteria, such as round-robin, best reported channel quality, proportionate fair, and the like. In addition to determining to which mobile terminal, or user, to transmit data packets at any given time, or slot, the base station must also limit the number of users in the queue or pool of users requesting data. This is known as admission control.
Admission control maintains the required integrity of services provided by the wireless system. Admission control avoids instability which may occur if system resources are over-allocated. Generally, admission control algorithms attempt to maximize the number of simultaneous active users while protecting the system from overload.
In cdma2000 1x, the forward link admission control for the packet data channel was performed based on the available residual power. In 1xEV-DO Rev. 0, the forward link admission control was performed based on the residual time slots. The number of unused time slots, or percentage of time slots utilized gave some indication of the performance per user; this metric was used to perform admission control. 1xEV-DO Rev. A allows multi-user packets, wherein a plurality of small data packets—possibly addressed to different users—may be bundled into a single transmission packet. With multi-user packets, forward admission control cannot be performed based on the availability of time slots, as this metric no longer correlates with the number of users being served (i.e., the number of users in the pool awaiting transmission of data packets).
However, admission control must still be performed in 1xEV-DO Rev. A so that the available resources are not over-utilized. Over-utilizing resources results in poor integrity of calls. For example, real time applications will experience excessive delay and best effort applications will experience low throughput. In order to avoid poor integrity, the system must perform admission control. In general, admission control may be performed by identifying shared resources, and monitoring the allocation of shared resources, and the impact on the shared resources of admitting a new user.